A conventional engine controller uses a governor pattern map to determine a directed governor pattern injection quantity based on an accelerator operation amount (accelerator opening) and an engine speed. Japanese Patent document JP-A No. 296470/1996 at pages 1 to 15 and FIGS. 1 to 10 discloses an engine controller controlling an injection quantity based on the directed governor pattern injection quantity. When the engine is accelerated, the engine controller calculates a directed acceleration correcting injection quantity based on a previously calculated directed basic injection quantity. Based on the directed acceleration correcting injection quantity, the engine controller controls the injection quantity to prevent variations in output torque of an engine shaft.
Another conventional engine controller calculates an engine output shaft torque (i.e., driver-requested torque) requested by a driver based on the accelerator operation amount and the engine speed. Japanese Patent document JP-A No. 317681/2002 at pages 1 to 6 and FIGS. 1 to 7 discloses an engine controller controlling either intake airflow or an injection quantity based on the driver-requested torque. Even when the engine warms up during cold startup or idles high due to external load operations such as an air conditioner, the accelerator operation amount is corrected using an offset map that includes correction amounts for the accelerator operation amount plotted against target revolution speeds during an idle operation. Even when the driver's accelerator operation amount is 0, the driver-requested torque never indicates a negative value. The engine idle speed after an increase in the idle is maintained.
The governor pattern described in JP-A No. 296470/1996 identified above identifies balancing characteristics between the engine speed and the accelerator opening for establishing a static engine output shaft torque. The governor pattern makes it impossible to directly achieve an intended parameter (target speed or acceleration). For example, there is a problem in requiring many steps compliant with drivability (steady and smooth driving performance or accelerating/decelerating driving performance) and increasing costs.
The engine controllers described above fail to provide one-to-one correspondence between physical phenomena such as vehicle specifications and stored data such as the governor pattern, control logic, or a control program. When a change is made to vehicle specifications such as the vehicle weight, the effective tire radius, the final change gear ratio, the air pressure coefficient, the frontal projected area, and/or the tire rolling resistance coefficient, it follows that a running resistance, a wheel (driving wheel) torque, and the engine output shaft torque also change. It is difficult to modify the stored data such as the governor pattern, the control logic, and the control program in view of these changes.
During a steady operational state, a change in the driver's accelerator operation amount is smaller than or equal to a specified value. The steady state may be defined by the driver driving at a constant target speed along a flat road. In a transient state, a change in the driver's accelerator operation amount is greater than or equal to the specified value. The transient state can be defined by the driver accelerating or decelerating at a target acceleration on a flat road.
As mentioned above, there may be a case where a driver-requested engine output shaft torque (i.e., driver-requested torque) is calculated based on the driver's accelerator operation amount. In such a case, it is desirable to calculate the torque while considering a running resistance and the vehicle specifications. Running resistance is generated when vehicles travel along roads due to the tires (driving wheels) contacting the road surface. Considering this makes it possible to achieve the driver-requested torque and the wheel (driving wheel) torque corresponding to the driver's accelerator operation amount. The vehicle is requested to travel at a target speed or a target acceleration smoothly and without passenger discomfort. For this purpose, it is desirable to calculate the driver-requested torque using correction amounts that take into consideration the running resistance, the wheel (driving wheel) torque, and the final gear ratio, which vary with changes in the vehicle specifications.
Vehicles of the same car model may be additionally equipped with, for example, aero parts, an air conditioning system, na electrically operated sunroof, a navigation system, parts compliant with cold region specifications, dealer installed optional parts, or other accessory drive devices. In such a case, the vehicle weight, which is a constant vehicle specification, is changed.
The above-mentioned running resistance is broadly categorized into air resistance, rolling resistance, hill-climbing resistance, and acceleration resistance. During constant travel on a flat road, the running resistance results from the sum of the air resistance and the rolling resistance. During travel along a slope, the hill climbing resistance is added. During acceleration and/or deceleration, the acceleration resistance is added.
In the above description, the air resistance is calculated based on a vehicle speed (V) detected by a vehicle speed sensor, an air resistance coefficient, and a frontal projected area uniquely predetermined by the vehicle specifications. The acceleration resistance is calculated based on a vehicle acceleration (αV) determined by differentiating the vehicle speed (V) detected by the vehicle speed sensor and a vehicle weight (W) uniquely predetermined by vehicle specifications.
When a change is made to a vehicle specification (vehicle weight, effective tire radius, final change gear ratio, air pressure coefficient, frontal projected area, tire rolling resistance coefficient), the running resistance, the wheel (driving wheel) torque, and the engine output shaft torque change. In the event of these changes, it is difficult to modify the stored data, the control logic, and/or the control program in the engine controller.